One important characteristic of nucleic acids, which form the genetic material of all living organisms, is their ability to form sequence-specific hydrogen bonds (that is, hybridize) with a nucleic acid having a complementary nucleotide sequence. This ability of nucleic acids to hybridize with complementary strands of nucleic acids has been used to advantage in what are known as hybridization assays, and in DNA purification techniques.
In a hybridization assay, a nucleic acid having a known sequence is used as a probe in a test sample to hybridize with a "target" nucleic acid having a complementary nucleic acid sequence. Labelling the probe allows for detection of the hybrid, and correspondingly, the target nucleic acid. Some hybridization assays are known as "sandwich" assays and involve the use of two probes, one labeled as noted above, and a second "capture" probe which is immobilized in some manner on a substrate (such as a filter, sheet or particle).
Because all strains of a particular organism or vital-infected cell share a genetic component in the form of nucleic acids, hybridization assays are valuable research and diagnostic tools for detection of and diagnosis of various disease states in humans, animals and plants. Additionally, the ability to probe for a specific nucleotide sequence is of potential value in the identification and diagnosis of human genetic disorders.
In the field of biochemistry and molecular biology, the purification or isolation of nucleic acids in a mixture thereof is often important for research and synthesis of genetic materials. A number of procedures have been developed whereby nucleic acids are isolated in affinity chromatography by using complementary strands attached to solid carriers.
The attachment of oligonucleotides to supports of various kinds has been accomplished in a number of ways, as noted for example in EP-B-0 070 687 (published Jan. 26, 1983) and references noted therein. Most of these techniques require the modification of the support or oligonucleotide or both in order to have suitable covalent bonding.
U.S. Pat. No. 4,713,326 (issued Dec. 15, 1987 to Dattagupta et al) describes binding nucleic acids to solid supports using a photochemically reactive intercalator compound such that upon irradiation, the nucleic acid is chemically linked to the support. Other linking groups, both photochemical or not, have also been used to connect oligonucleotides to solid supports, such as particles (see for example, WO-A-88/01302, published Feb. 25, 1988).
In some instances, nucleic acids can be directly attached to particles to prepare probes such as when the particles have surface carboxylic acid groups. However, this is not always easy nor convenient. Moreover, due to the hydrophobic nature of the particles having such reactive groups, and the nature of the oligonucleotides, molecules of the oligonucleotides adsorb to the particles after being covalently attached thereto. Such adsorption prevents efficient hybridization of the oligonucleotide with complementary nucleic acids.
It would be desirable to have an efficient means for hybridization or purification of nucleic acids using a water-insoluble probe.